Prefer centralized configuration objects over environment variables for application settings. Environment variables create inconsistent configuration sources and can lead to maintenance challenges. Guidelines: - Use a single, centralized `Config` structure as the "one true way" to configure your application - When adding new settings, place them in the appropriate configuration structure rather than reading from environment variables - Reserve environment variables primarily for bootstrap settings or when absolutely required For feature flags or experimental options, use structured configuration with appropriate prefixes: ```rust // Preferred config.experimental_resume = true; // Instead of if std::env::var("CODEX_EXPERIMENTAL_RESUME").is_ok() { ... } ``` When environment variables must be used: - Load them as early as possible in the application lifecycle before any threads are created - Document the thread-safety implications clearly - In tests, configure components explicitly rather than modifying process-wide environment variables Remember that modifying environment variables is inherently racy in multi-threaded contexts and has been marked as `unsafe` in recent Rust editions.